Nothing can be taken for granted with the Covid-19 pandemic. The coronavirus is constantly evolving, mutating and creating new variants. Rules and restrictions perceived as being adequate to protect society one week may not be as effective the next. Confirmation that two Hong Kong-based pilots have been infected after overseas travel is reason to reassess whether quarantine-free exemptions for aircrew are still in the interests of public health. The pilots tested positive for the highly infectious Delta variant three days after returning on a Cathay Pacific cargo flight from Frankfurt last Saturday. They were fully vaccinated, but the viral load of one, aged 29 and living in Tsim Sha Tsui, was high. The finding, made during compulsory screening, prompted testing of thousands of people from dozens of places they and family or friends had visited and quarantining of hundreds. Among affected locations were Ocean Park, the ferry piers and Discovery Bay International School, which was closed while staff and students were quarantined and tested; the other pilot’s wife is a teacher there and both his sons are pupils. Aircrews are among groups exempt from compulsory quarantine under tightened government requirements that take effect today. Authorities, trying to more closely align Hong Kong’s Covid-19 strategy with the mainland’s to enable a resumption of cross-border travel, on November 1 slashed the number of people able to move freely without the need for isolating in designated facilities for either 14 or 21 days. Only categories perceived as essential to the operation of society and the economy were spared. Those involved in transporting daily necessities were, along with senior government officials, given a pass; apart from crews of aircraft and ships, they include drivers of cross-boundary goods vehicles and buses. Hong Kong may restrict aircrew movements in light of pilot Covid-19 cases Hong Kong has adopted the mainland’s zero-tolerance approach towards the coronavirus and maintains some of the world’s toughest restrictions. But many other governments have decided that it will not be possible in the short term to eradicate the disease and have opted to live with it and reopen for overseas travel. New variants such as Delta mean that even those who are inoculated with the most effective vaccines are still vulnerable. But even though authorities know the importance to the economy of foreign companies and corporations, they have to take care about how they deal with the outside world if mainland travel is the priority. A regimen of prompt testing, tracing and quarantining has worked well for Hong Kong; there has been no local infection for weeks or outbreaks for months. Every loophole has to be closed if that is to continue. The positive tests of the cargo pilots are reasons for a review of aircrew exemptions.